Windrower header floatation system having assisted downforce control with downforce return valve

Abstract

An agricultural machine includes a float cylinder interconnecting a header linkage system and a frame. A rod side accumulator is in fluid communication with a rod side fluid port of the float cylinder. A float control valve is selectively controllable between an open position allowing fluid communication between a pressure source and the rod side accumulator, and a closed position blocking fluid communication between the pressure source and the rod side accumulator. A downforce accumulator is in fluid communication with a piston side fluid port of the float cylinder. A downforce control valve controls fluid communication between the pressure source and the downforce accumulator. A downforce return valve controls fluid communication between the downforce accumulator and the tank.

1 . An agricultural machine comprising:
 a frame;   a header linkage system attached to the frame and configured for attaching a cutter head to the frame;   a tank operable to store a supply of a fluid;   a pressure source in fluid communication with the tank and operable to receive fluid from the tank and circulate the fluid through a fluid circuit;   a float cylinder interconnecting the header linkage system and the frame, the float cylinder including a rod side fluid port in fluid communication with the pressure source for receiving fluid from the pressure source to retract the float cylinder, and a piston side fluid port;   a downforce accumulator in fluid communication with the piston side fluid port of the float cylinder; and   a downforce return valve in fluid communication with the downforce accumulator and the tank, wherein the downforce return valve is selectively controllable between an open position allowing fluid communication between the downforce accumulator and the tank, and a closed position blocking fluid communication between the downforce accumulator and the tank.   
     
     
         2 . The agricultural machine set forth in  claim 1 , further comprising a downforce control valve in fluid communication with the pressure source and the downforce accumulator, wherein the downforce control valve is selectively controllable between an open position allowing fluid communication between the pressure source and the downforce accumulator, and a closed position blocking fluid communication between the pressure source and the downforce accumulator. 
     
     
         3 . The agricultural machine set forth in  claim 2 , wherein the downforce return valve and the downforce control valve are separate and independently operable relative to each other. 
     
     
         4 . The agricultural machine set forth in  claim 1 , further comprising a header controller configured to control the downforce return valve to the open position to operate the header linkage system in a lift operating condition, and control the downforce return valve to the closed position to operate the header linkage system in a float operating condition. 
     
     
         5 . The agricultural machine set forth in  claim 1 , further comprising a rod side accumulator in fluid communication with the rod side fluid port. 
     
     
         6 . The agricultural machine set forth in  claim 5 , wherein the downforce accumulator defines a piston side volume that is compressible in response to a fluid pressure above a defined piston side set point, and the rod side accumulator defines a rod side volume that is compressible in response to a fluid pressure above a defined rod side set point, wherein the piston side set point is different than the rod side set point. 
     
     
         7 . The agricultural machine set forth in  claim 5 , further comprising a float control valve in fluid communication with the pressure source and the rod side fluid port of the float cylinder, wherein the float control valve is selectively controllable between an open position allowing fluid communication between the pressure source and the rod side fluid port of the float cylinder, and a closed position blocking fluid communication between the pressure source and the rod side fluid port of the float cylinder. 
     
     
         8 . The agricultural machine set forth in  claim 7 , wherein the rod side accumulator is disposed within the fluid circuit between the rod side fluid port and the float control valve. 
     
     
         9 . The agricultural machine set forth in  claim 1  further comprising a system return line interconnecting an output of the pressure source and the tank in fluid communication. 
     
     
         10 . The agricultural machine set forth in  claim 9 , further comprising a return valve in fluid communication with the system return line, wherein the return valve is selectively controllable between an open position allowing fluid communication through the system return line and a closed position blocking fluid communication through the system return line. 
     
     
         11 . The agricultural machine set forth in  claim 7 , wherein the float cylinder is a double acting hydraulic cylinder operable to extend in response to receiving fluid into the piston side fluid port via the downforce control valve and retract in response to receiving fluid into the rod side fluid port via the float control valve. 
     
     
         12 . The agricultural machine set forth in  claim 1 , further comprising a lift cylinder interconnecting the header linkage system and the frame, the lift cylinder including a rod side fluid port in fluid communication with the pressure source for receiving fluid from the pressure source to retract the lift cylinder, and a piston side fluid port in fluid communication with the tank. 
     
     
         13 . The agricultural machine set forth in  claim 12 , further comprising a lift control valve in fluid communication with the pressure source and the rod side fluid port of the lift cylinder, wherein the lift control valve is selectively controllable between an open position allowing fluid communication between the pressure source and the rod side fluid port of the lift cylinder, and a closed position blocking fluid communication between the pressure source and the rod side fluid port of the lift cylinder. 
     
     
         14 . The agricultural machine set forth in  claim 2 , further comprising a downforce supply line including the downforce control valve, and a downforce return line including the downforce return valve. 
     
     
         15 . The agricultural machine set forth in  claim 2  wherein the downforce control valve and the downforce return valve are combined as a single combined downforce control valve unit including a first position connecting the pressure source and the downforce accumulator in fluid communication while simultaneously blocking fluid communication between the downforce accumulator and the tank, a second position blocking fluid communication between the downforce accumulator and both the pressure source and the tank, and a third position connecting the tank and the downforce accumulator in fluid communication while simultaneously blocking fluid communication between the downforce accumulator and the pressure source. 
     
     
         16 . An agricultural machine comprising:
 a frame;   a header linkage system attached to the frame and configured for attaching a cutter head to the frame;   a fluid circuit configured for operating the header linkage system in a float operating condition and a lift operating condition, wherein the fluid circuit includes:
 a tank operable to store a supply of a fluid; 
 a pressure source in fluid communication with the tank and operable to receive fluid from the tank and circulate the fluid through the fluid circuit; 
 a lift cylinder interconnecting the header linkage system and the frame and controlled to extend or retract during operation in the lift operating condition, the lift cylinder including a rod side fluid port in fluid communication with the pressure source, and a piston side fluid port in fluid communication with the tank; 
 a float cylinder interconnecting the header linkage system and the frame and operable to extend and retract during operation in the float operating condition, the float cylinder including a rod side fluid port in fluid communication with the pressure source, and a piston side fluid port in fluid communication with the pressure source; 
 a downforce accumulator in fluid communication with the piston side fluid port of the float cylinder, the downforce accumulator defining a piston side volume that is compressible in response to a fluid pressure above a defined piston side set point; and 
 a downforce return valve in fluid communication with the downforce accumulator and the tank, wherein the downforce return valve is selectively controllable between an open position allowing fluid communication between the downforce accumulator and the tank, and a closed position blocking fluid communication between the downforce accumulator and the tank. 
   
     
     
         17 . The agricultural machine set forth in  claim 16 , wherein the fluid circuit includes a downforce control valve disposed between the downforce accumulator and the pressure source, wherein the downforce control valve is selectively controllable between an open position allowing fluid communication between the pressure source and the downforce accumulator to operate the header linkage system in a first float condition exhibiting a first header float return speed, and a closed position blocking fluid communication between the downforce accumulator and the tank to operate the header linkage system in a second float condition exhibiting a second header float return speed, wherein the first header float return speed is less than the second header float return speed. 
     
     
         18 . The agricultural machine set forth in  claim 16 , wherein the fluid circuit includes a rod side accumulator in fluid communication with the rod side fluid port of the float cylinder, the rod side accumulator defining a rod side volume that is compressible in response to a fluid pressure above a defined rod side set point. 
     
     
         19 . The agricultural machine set forth in  claim 16 , wherein the fluid circuit includes a float control valve disposed between the pressure source and the rod side fluid port of the float cylinder, wherein the float control valve is selectively controllable between an open position allowing fluid communication between the pressure source and the rod side fluid port of the float cylinder, and a closed position blocking fluid communication between the pressure source and the rod side fluid port. 
     
     
         20 . The agricultural machine set forth in  claim 16 , wherein the fluid circuit includes a lift control valve in fluid communication with the pressure source and the rod side fluid port of the lift cylinder, wherein the lift control valve is selectively controllable between an open position allowing fluid communication between the pressure source and the rod side fluid port of the lift cylinder, and a closed position blocking fluid communication between the pressure source and the rod side fluid port of the lift cylinder.